PURPOSE: To make the demodulation characteristic stable and to improve the mass-productivity by using a microstrip line for an inductor forming a resonance circuit for a voltage controlled oscillator so as to concentrate an oscillating power into a printed circuit board to the utmost and not emitting the power to the rear side.

CONSTITUTION: A voltage controlled oscillator 18 is oscillated by a resonance circuit comprising at least varactor diodes 40, 41 and microstrip lines 75, 76. In this case, the microstrip lines 75, 76 whose length is nearly equal to each other are connected between balance input terminals of an active circuit comprising a differential amplifier coupled with positive feedback by using a capacitor 4, and the varactor didoes 40, 41 are connected to the two microstrip lines 75, 76 to form the resonance circuit. Thus, the differential amplifier is oscillated while keeping the differential balance. Thus, the common mode component is not produced to the utmost from the oscillation signal from the voltage controlled oscillator 18. Then the oscillated power is almost concentrated onto a dielectric material of the microstrip lines.